// https://www.cnblogs.com/kevinCoder/p/4572201.html
var a = 'A'.charCodeAt();
console.log(a);  //65

var b = '0'.charCodeAt();
console.log(b); //48

var c = 'a'.charCodeAt();
console.log(c); //97

var d = 'abc'.charAt(0);
console.log(d); //a

var e = 'abc'.charAt(1);
console.log(e); //b

var f = 'abc'.charAt(2);
console.log(f); //c
